The present invention relates to a colored product of a porous fluorocarbon resin material and a method for its manufacture, specifically for the purpose of achieving the coloring with brightness and fastness to various factors while avoiding any substantial degradation of the excellent gas and moisture permeability and water proofing properties inherent in porous fluorocarbon material of continuous porosity.
Generally fluorocarbon resins, represented typically by polytetrafluoroethylene (hereinafter abbreviated as PTFE), are excellent for their thermal and chemical resistance, surface slipperiness and other properties when compared with other resins and are processed by various methods to produce products of various types for wide use in a wide range of applications.
The porous fluorocarbon resin material having continuous porosity (hereinafter referred to simply as the porous fluorocarbon resin material), which makes possible the coloring object of the present invention, itself has extensive applications. For example, the porous material of PTFE is excellent in softness, lightness, gas and moisture vapor permeability, waterproofness, touch, handling and other properties in addition to other excellent properties inherent in the said resin. This material is utilized, for example, as a material for various artificial body organs such as blood vessels, for patches and oxygenating membranes and for medical equipment such as diaphragms of various types, filters, flexible packings, etc. Also, PTFE in the form of a thin porous film is utilized, after being laminated with a woven or nonwoven base cloth, for jackets and feathercoats or other clothes which require gas and moisture vapor permeability characteristics together with waterproofness. The method of manufacture of the porous material of PTFE used in this invention is known, for example in Japanese Patent Publication No. Sho-48-44664 (1973), Japanese Patent Disclosure No. Sho-46-7284 (1971) and Japanese Disclosure Sho-50-2281 (1975). It is possible to manufacture expanded porous PTFE material in the form of sheet, tube, bar, filament and other various types by baking or thermo-setting at an elevated temperature (200.degree. C.-327.degree. C.). By varying the stretch ratio and other manufacturing conditions, the properties of the porous products may be controlled. Porosity, average pore size, Gurley number and thickness can be produced in the ranges of about 20-90%, 0.01-30 microns, 0.01-5000 seconds and 0.005 millimeters minimum, respectively. Thus, a material suitable for the object of this invention can be obtained easily. It is noted that "Gurley" number represents the time required for 100 cc of air to permeate a section of material having a diameter of 2.54 cm under a pressure of 12.7 mm H.sub.2 O pressure.
However, since the excellent chemical resistance, water repellency and other properties of fluorocarbon resins result in poor dyeability, the said resins, solid or porous, usually have poor color properties, and it is very difficult to obtain a good, colored product.
In view of the above, the inventor previously offered a method for satisfactorily coloring porous materials of fluorocarbon resins (Japanese Patent Disclosure No. Sho-53-60949 (1978). In that method, the porous fluorocarbon resin material was impregnated with a solvent solution of a resin which produces the dyeing sites, i.e. a resin which has excellent dyeability. The impregnated material was dried and then dyed; or, the porous fluorocarbon resin material was impregnated with a solution containing that resin which makes the dyeing sites and a dyestuff, then dried.
Thus, when the porous fluorocarbon resin material was impregnated with the resin that produces the dyeing sites and was dried, the solvent of the resin solution was evaporated leaving the solid resin, thinly coating in a continuous manner, all the circumferential surfaces of fine fibers and nodes of complex fibril tissues which form the framework of the respective fine pores of the porous fluorocarbon material, and therefore, even though the residual resin and the fluorocarbon resin do not adhere to each other well, the said residual resin will no longer easily fall off under this condition because it encloses and coats continuously and thinly the respective fibers and nodes of the porous material. In addition, since the resin coating is thin and does not clog the pores of the porous, fluorocarbon material, no characteristics inherent in the porous tissue would be impaired.
Therefore, when the porous fluorocarbon resin material, impregnated with a resin solution which produces the said dyeing sites is dried and then dyed according to the previous method, the dyeing-site resin will easily be dyed bright, so that the entire porous fluorocarbon resin material could be colored bright and fast without substantial degredation of the characteristics inherent in the porous material. After the dyeing, any residual dyestuff present in excess or unfixed was removed by washing. Drying the prepared material produced the colored final product.
When the resin solution was added with the dyestuff beforehand, a porous product which was colored bright and fast was obtained by impregnating the porous fluorocarbon resin material by the said solution and subsequently drying. In that case, the final colored product was then prepared by washing and drying.
In view of the above coloring principle, the dyeing-site resin solution used in the above method of the previous invention had the following requirements:
(a) It smoothly permeates the fine fibril tissue of the porous material, i.e. the porous matrix.
(b) The resin content of the resin solution which has permeated the porous matrix and which has covered the outer surfaces of the porous material will be left, after drying, in the form of a thin coating film around each fine fiber and fine node of the porous fibril matrix. Thus, in order to retain substantially the gas permeability of the porous material, neither pores in the matrix nor pore openings in the surface of the porous material will be clogged by the resin film (the continuously coating resin film layer).
It was essential, therefore, to use a resin solution of rather low concentration, and in that method the concentration of the resin solution was limited practically to as low a value as possible, about 10% at the most. Thus, the mixing dose of the dyestuff was also limited.
Nevertheless, there is a very close correlation between the dyeing-site resin and the resulting dyeing brightness. That is, the larger the resin dose, the better the dyeing brightness. In addition to the dyeing brightness, the dyeing fastness improves generally with increases in resin dose. For example, it is known that degradation by light of the dyeing fastness increases with decreasing resin dose.
Even though the prior dyeing method has a coloring effect much better than any previous conventional method, there was a certain limit to improvement in dyeing brightness and fastness due to the said limit in the application dose of resin and dyestuff.
Using the same dyeing-site resin and dyestuff, the present invention enables the use of increased doses and offers a colored, porous fluorocarbon resin material having not only an adequate gas and moisture permeability and waterproofing property but also better dyeing brightness and fastness than the method of the previous invention mentioned above. This also applies to its manufacturing method.